This disclosure relates to steer-by-wire vehicle control systems.
Steering equipment for assisting a driver to steer an automobile is well known in the art. In conventional steering assemblies, the operator controls the direction of the vehicle with the aid of a steering wheel. This wheel is mechanically connected, usually through a gear assembly to the roadwheels. To aid the operator, many systems utilize a an auxiliary system to generate a force that is transmitted to a steering gear assembly. The additional force reduces the effort required by the operator in changing the direction of the vehicle. Typically, this auxiliary force is generated by either a hydraulic drive or an electric motor.
Because the steering wheel is connected directly to the roadwheels, the resulting mechanical assembly that provides the connection can be quite complicated and expensive to produce. The one advantage in having a direct connection is that the operator receives tactile feedback through the steering wheel. For example, if the vehicle changes directions while it is moving, the operator will feel resistance in the steering wheel.
Therefore, is it considered advantageous to provide a steering control system that is less expensive than a traditional mechanical system while still providing the tactile feedback to the operator.
The present invention is directed to a control system that provides a vehicle operator with an electronic steering or steer-by-wire control for a vehicle. The steer-by-wire control system comprises a roadwheel unit, a steering wheel unit, and a master control unit that operate together to provide steering control for the vehicle operator. The roadwheel unit has several sensors including a roadwheel position sensor and a tie-rod force sensor that are used to provide a signal to the master control unit. The steering wheel unit has a sensor for detecting steering wheel position, this sensor is used to provide a signal to the master control unit. Signals from the sensors in the roadwheel unit and steering wheel unit are received by the master control unit where they are used to calculate roadwheel command signals and steering wheel reaction torque signals. The resulting roadwheel command signal is sent back to the roadwheel unit to change the direction of the vehicle, while the steering wheel reaction torque signal is sent to the steering wheel unit where it is used to provide tactile feedback to the vehicle operator. The present invention also utilizes an Ackerman correction control to adjust the left and right roadwheel angles to correct for errors in the steering geometry so that the wheels will track about a common turn center.